const animals = {};
let dog = { emoji: "dog" };
let cat = { emoji: "cat" };

animals[dog] = { ...dog, name: "Mara" }; //? 以dog为key 转换为字符串是"object Object"
animals[cat] = { ...cat, name: "Sara" }; //? 同理 覆盖了前面的key值

console.log(animals[dog]);
